Two cases of pressure ulcers related to acute calcium pyrophosphate crystal arthritis: A new concept of "disease-specific unexpected external forces".

Sudden-onset immobilisation generates unexpected external forces over bony prominences and is a potential cause of pressure ulcers. Here, we report two cases of deep pressure ulcers in patients with acute monoarthritis as a result of calcium pyrophosphate (CPP) crystal deposition (pseudogout). The patients were women in their 80 who could perform activities of daily living by themselves. They developed pressure ulcers while living in their own home. Because acute CPP crystal arthritis is known to develop in relatively healthy elderly patients, patients and caregivers do not expect sudden-onset immobilisation. In addition, larger joints are preferentially involved in acute CPP crystal arthritis, leading to the inability of patients to change positions themselves. Therefore, acute CPP crystal arthritis should be recognised as a potential causal disease for pressure ulcers. This case report further highlights a new concept of "disease-specific unexpected external force", which is beneficial for the prevention of pressure ulcers.